Natural vs. Synthetic rubber foam ? search project solution help

Hello everybody
I have a mass production project for a new product .
The thing is to be made in foam , sheets...it is some material involved .
To visualize the idea think about the Yoga mat sort of material but much thick..

Natural or Synthetic ?..provided there is to be found a natural rubber foam sheet that thick on the market , any market , and at what price (?!)..